1. Field of the Invention
The present invention relates generally to an improved small-sized disk unit, and more particularly to a connection structure by means of FPC""s (flexible printed circuits) between a head and an IC, a RAM storage of various types of offset correction values, position sensitivity measurement processing and a small-sized disk unit which generates sector pulses allowing for encode loss in write operation and decode loss in read operation.
2. Description of the Related Art
With a recent remarkable reduction in cost of magnetic disk units, cost-effective production and assembly are also pressingly desired. In conventional techniques, connection is made as follows between a head IC mounted FPC which is disposed on a base and a head which is supported at the distal end of a head actuator. A flexible read/write FPC band is extended from the head IC mounted FPC. A relay FPC extending from the head on the other hand is adhesively joined to the lateral surface of a head arm of the actuator. Land areas with terminal patterns of the two FPC""s are fixedly joined together in a superposed manner on the lateral surface of the head arm. In the conventional FPC attachment structure, however, since-the terminal ends of two FPC""s are electrically and mechanically connected together in a superposed manner on a flat mounting surface of the head arm, the land area of the FPC on one hand is adhered securely to the mounting surface whereas the land area of the FPC on the other is superposed thereon in a raised state relative to the mounting surface. In this manner, connection surfaces of the two FPC""s do not lie in the same plane, which may subject the land areas to a positional offset upon the superposition, thus necessitating a high-precision positioning and increasing the number of working steps. This may preclude a sufficient curtailment in production and assembly costs.
It is also anticipated that the magnetic disk unit may be used in a place subjected to an extreme variation in environmental temperature and humidity, and hence various types of head position corrections are effected in order to ensure a normal operation. In this case, closer positions of cylinders subjected to such head corrections will lead to a higher precision correction. In order to provide closer cylinder positions to secure a higher precision correction, however, the capacity of the RAM for storing correction values therein must be larger, which will prevent the costs from being lowered. It is thus desired to provide a correction capable of reducing the use capacity of the RAM without impairing the precision of correction. In the conventional magnetic disk unit, the entire cylinder range of a disk medium is divided into a plurality of zones at equal intervals, and correction values at zone boundaries are measured and stored in the memory. Correction for arbitrary positions within a zone whose correction values have not been measured and stored are found by means of a linear interpolation from the correction values at opposite zone boundaries which have been stored. However, the correction values for the cylinder positions may often present nonlinear characteristics. In the case of dividing into a plurality of zones at equal intervals, the zone intervals must be closer in order to ensure an accurate measurement of the non-linear portion. This will result in closer zone intervals in the linear portion and hence an increase in capacity of the memory for storing the measured correction values, thus bringing about an increase in costs. For the realization of cost-savings, in recent years in particular, a reduced capacity RAM is used as an internal memory of an MCU for use in a disk controller. This has a smaller RAM area available for the storage of the correction values. Efficient storage of the correction values is thus desired.
On the contrary, recent magnetic disk units tend to employ a closer track pitch with the reduction in size and increase in capacity, and hence the improvement in on-track precision is desired. Also, due to the employment of an MR head having a small core width as the read head in contrast with the write head using an inductive head, a core offset correction is inevitable between the write head and the read head. Thus, a phase variation position may become an on-track position. For this reason, in place of the conventional phase variation of two-phase servo pattern at a half track pitch, two-phase servo information is proposed in which the phase varies at one-third pitch. In order to effect the measurement of position sensitivity correction values in the conventional disk unit, it is necessary to measure a cross point of the two-phase servo signals N and Q. It is however impossible to directly measure the cross point since the servo signals N and Q are discretely obtained for each of sample cycles. A value of the cross point has thus been determined by means of a linear interpolation from values anterior and posterior to crossing the cross point of the two-phase servo signals N and Q which can be obtained when performing an equal-speed seek. An error may therefore be involved therein. In the case of the two-phase servo signals in which the track pitch is reduced to allow the phase to vary at one-third track pitch, two cross points appear during one track displacement. This means that the cross point density is doubled as compared with the case of a half track pitch. Thus, too much time is disadvantageously required for the measurement of the position sensitivity correction values, and it was difficult to expect to improve the measurement precision due to the linear interpolation.
To implement a size reduction and capacity increase of the disk unit, miniaturization of the disk size is advanced with the employment of disk-high density recording for the increase in capacity. Also, for the read and write signal processing system, a partial response most likelihood (PRML) method is employed to heighten the function. With such heightening of function of the signal processing system, encode and decode time loss which could have been neglected for the conventional 1-7RLL, etc. tends to be increased. In the 1-7RLL for example, it was merely of the order of five bits. However, the partial response most likelihood method based signal processing entails as much as44 bit loss, which is about ten times the former loss. A gap region for accommodating the loss must be provided and hence the format efficiency may be lowered. In the case of a conventional format allowing for both the encode loss and decode loss, in particular, the format efficiency will be remarkably lowered since it is provided with a gap region corresponding to the sum of the encode loss and the decode loss, the encode loss meaning an elongation of time taken in write operation after the completion of NRZ data input until the completion of write into the disk medium, the decode loss meaning an elongation of time taken in read operation after the acquisition of read signal until the actual NRZ data demodulation output.
According to a first aspect of the present invention, there is provided a disk unit having a structure ensuring an easy positioning, on a mounting surface of an actuator, of a base-side read/write FPC and a head-side relay FPC. More specifically, on the FPC mounting surface of the head actuator, a land area with a connection pattern of a read/write. FPC band extending from a base-side FPC is superposed fixedly for connection on a land area with a connection pattern of a relay FPC attached to the head. In this case, an FPC mounting surface of the head actuator is formed with a recessed step on the read/write FPC band side, and in a state where the land area of the read/write FPC has been disposed in the recessed portion of this step so as to be level with the FPC mounting surface of the head actuator, the read/write FPC band land area is superposed fixedly for connection on the relay FPC land area. The read/write FPC band is received in the step formed in the FPC mounting surface, together with an underlying retainer serving as a support member. According to this FPC attachment structure, the recessed step accommodates the thickness of the read/write FPC band and the retainer as the support member, allowing the land areas of the read/write FPC band and the relay FPC to rest on the same plane, thus eliminating any step on a connection plane. As a result, there is no step between the two FPC land areas which are joined together in a superposed manner, ensuring an easy positioning work and improved positioning accuracy.
According to a second aspect of the present invention, there is provided a disk unit capable of arbitrarily varying the intervals of zones which store and hold measured correction values and minimizing the use capacity of the RAM which stores zone correction values. The object of the present invention is a disk unit which detects a head position on the basis of servo information stored on a disk medium and corrects for control the head position using predetermined offset correction data which have been defined in advance for each head position. In the present invention, such a disk unit is provided with a ROM table having a plurality of memory areas for storing therein pointer information which are allocated to a plurality of zones obtained by dividing a storage area of the disk medium, and a RAM table whose one or more memory areas are designated by each pointer information of ROM table and store offset correction data of a head position corresponding to each pointer information. The offset correction data generation unit finds pointer information through a reference to the ROM table, on the basis of a zone derived from a current head position X relative to the disk medium, refers to the RAM table using this pointer information to acquire offset correction data, and generates offset correction data at a current head position X through an interpolating calculation of the thus acquired offset correction data. Herein, the ROM table includes a plurality of memory areas corresponding to a plurality of equally divided zones, and the zones having the same offset correction data store the same pointer information, allowing an acquisition of the same pointer designated offset generation data stored in the RAM table. The RAM table stores offset correction data for one boundary position of each of a plurality of zones obtained by division. In this case, if the current head position lies in for example a zone Zi, then the offset correction data generation unit acquires first offset data G2 at one zone boundary position through a zone Zi based reference to the ROM table and RAM table. Then, the value of the zone for use in a reference to the ROM table is incremented by one into Zi+1. The offset correction data generation unit acquires second offset correction data at the other boundary position through a zone Zi+1 based reference to the ROM table and RAM table, and calculates by means of linear interpolation the offset correction data at a current head position on the basis of the first and second offset correction data, zone intervals and the current head position.
The offset correction data stored in the RAM table can be
I. External force offset correction data for correcting a mechanical external force applied to the head actuator;
II. Position sensitivity correction data, which are used when transforming head position data generated from a read signal of servo information recorded on a disk medium, into a theoretically correct head position data;
III. BL correction data for correcting the effect of BL (product of magnetic flux B and coil length L) depending on a magnetic force of a motor for driving the actuator.
The ROM table and the RAM table comprise a ROM element and a RAM element, respectively, incorporated in a micro control unit of a disk controller. Servo information recorded on the disk medium comprises a servo surface servo in which servo information is recorded on an exclusive disk surface, or a data surface -servo in which servo information is recorded in an embedded manner within each sector of data surface. It is thus possible to vary the intervals for correction and to minimize the use area of the RAM, by using the pointer information of the ROM table so as to allow an arbitrary designation of a storage position in the RAM table which stores therein the correction data.
According to a third aspect of the present invention, there is provided a disk unit intended to transform, using position sensitivity correction values which have been measured in advance, two-phase servo signals N and Q detected from a read signal of two-phase servo information recorded on a.disk surface, into correct head position information. To this end, in the disk unit of the present invention, the disk medium has a disk surface on which the two-phase servo information is recorded in such a manner that the phase varies at one-third cylinder pitch. The position sensitivity. measurement unit executes, when measuring the position sensitivity correction value, on-track control at a cross point of two-phase servo signals N and Q derived from the servo information, and measures a value of the cross point to obtain a position sensitivity correction value. Herein, the position sensitivity measurement unit finds a measurement value at a position of the cross point on positive side and a measurement value at a position of the cross point on negative side two tracks apart therefrom, and calculates the position sensitivity correction value in the form of a mean value of absolute values of the two measurement values. This will relax asymmetry in the vertical direction of read waveforms of the MR head. The position sensitivity measurement unit calculates, as a position sensitivity correction value, a correction coefficient for correcting the cross point measurement value into a theoretical value. The position sensitivity measurement unit divides a recording area into a plurality of zones, and measures and stores a position sensitivity correction value for each of zone boundary positions, and upon a head position control, finds a position sensitivity correction value for a current position, through a linear interpolation, from position sensitivity correction values at two boundary positions of a zone in which a head is located.
According to a fourth aspect of the present invention, there is provided a disk unit capable of improving lowering of format efficiency attributable to encode loss and decode loss. The disk unit records a sector mark at a leading position of each of a plurality of sectors which are obtained by dividing tracks of a disk medium, and upon read operation or write operation relative to the disk medium, generates a write gate signal or a read gate signal on the basis of a sector pulse derived from a read of the sector mark. In order to improve lowering of the format efficiency caused by the encode loss and decode loss, the disk unit of the present invention comprises a gap region provided at the trailing position of each sector of the disk medium and having a duration corresponding to encode loss attributable to a write operation. The write gate generation unit generates in write operation a write gate signal in synchronism with the sector pulse, and stops the write gate signal in response to a detection signal of the gap region. The read gate generation unit generates in read operation a read gate signal in synchronism with a sector pulse with a delay of time corresponding to decode loss attributable to a read operation, and stops the read gate signal in response to a signal which is obtained by delaying the detection signal of the gap region by the time corresponding to decode loss. For this reason, a gap region corresponding to only the encode loss in write operation will suffice for the gap region of each sector. Thus, as compared with the conventional case of providing a gap region corresponding to the sum of the encode loss and decode loss, lowering of format efficiency can be improved with the increased disk capacity. The encode loss and decode loss vary depending on the cylinder positions, and the gap region having a duration corresponding to encode loss and the delay time corresponding to decode loss are each to be set to a value depending on a cylinder position of the head, for example, a value defined on a zone-by-zone basis.